I am learning seamless pattern creation in Illustrator CS6. I've created some repeated pattern and divide it by rectangle using the Object-Path-Divide objects below menu. Unexpectedly, there is some dislocation of the cut shapes relatively to background which was used as a cutter - I've copied the background rectangle and put it above the all elements (without fill or stroke). Look at the picture.
Is it my fault or it should be some bug within AI?
UPD1 The machine is MacBookPro and coordinates of the rectangle are as 160.466 px - could it be related to alignment issue/grid?